This application claims the priority of Japanese Application No. 8-262748, filed Oct. 3, 1996, and Japanese Application No. 8-283670, filed Oct. 26, 1996, the disclosures of which are expressly incorporated by reference herein.
The present invention relates to a semiconductor type sensor for detecting a pressure as a change in electrostatic capacitance and, more particularly, to a surface device type complex sensor which has sensors formed entirely on the same surface of a silicon chip.
As disclosed in Japanese patent document JP A No. 1-256177, a conventional complex sensor is a bulk type piezo-resistance sensor in which a differential pressure sensor, a static pressure sensor and a temperature sensor are formed on a single substrate, which is worked from the backside surface into a diaphragm.
In the conventional complex sensor of bulk type, since the silicon substrate is worked from the backside surface into a diaphragm, the position of the diaphragm is apt to deviate slightly from the sensing elements formed on the front surface of the silicon substrate. The sensitivity of the sensor would be substantially reduced even if there is a small deviation in the relative position. Therefore, in order to avoid this problem, it has been necessary to design the diaphragm on a relatively large scale. This is because positioning accuracy of the process for forming the sensors on both sides of the silicon wafer is lower than positioning accuracy for the formation of sensors on only one side of the substrate.
In addition, the conventional complex sensor has a high manufacturing cost because the silicon wafer must be mirror-finished on the both surfaces. Further, the piezo-resistance type sensor has a non-linear characteristic, and accordingly varies significantly with change in environmental temperature. Therefore, characteristic compensation of the sensor becomes more difficult, and the cost increases.
Japanese patent document JP A 4-143628 discloses electrostatic capacitance type pressure sensors each utilizing a silicon tip. However, it does not disclose any pressure sensors in which multi-function sensor portions are formed on only one side.
Japanese patent document JP A 5-187947 also discloses electrostatic capacitance type pressure sensors each utilizing a silicon chip. However, it does not disclose any pressure sensors each of which has pressure portions formed on only one side.
Further, conventional electrostatic capacitances or sensors are known which comprises a movable electrode of a flat member, a fixed electrode, an insulating film and a support for supporting the movable electrode to provide a gap between the movable electrode and fixed electrode. When a pressure is applied on the movable electrode, the movable electrode deflects so that displacement of the movable electrode is greatest at the center and is smaller toward the periphery. Therefore, the relationship of the electrostatic capacitance to the pressure is non-linear, and the non-linearity causes output errors.